Methods for growing a nitrogen doped single crystal silicon ingot using continuous czochralski method

ABSTRACT

A method for growing a single crystal silicon ingot by the continuous Czochralski method is disclosed. The melt depth and thermal conditions are constant during growth because the silicon melt is continuously replenished as it is consumed, and the crucible location is fixed. The critical v/G is determined by the hot zone configuration, and the continuous replenishment of silicon to the melt during growth enables growth of the ingot at a constant pull rate consistent with the critical v/G during growth of a substantial portion of the main body of the ingot. The continuous replenishment of silicon is accompanied by periodic or continuous nitrogen addition to the melt to result in a nitrogen doped ingot.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of U.S. application Ser.No. 16/569,949, which was filed Sep. 13, 2019, the disclosure of whichis hereby incorporated by reference as if set forth in its entirety.

FIELD OF THE DISCLOSURE

The field of the disclosure relates to a method to grow a single crystalsilicon ingot using the continuous Czochralski method and to a singlecrystal silicon ingot grown by this method.

BACKGROUND

Single crystal silicon, which is the starting material for mostprocesses for the fabrication of semiconductor electronic components, iscommonly prepared by the Czochralski (“Cz”) method. In this method,polycrystalline silicon (“polysilicon”) is charged to a crucible andmelted, a seed crystal is brought into contact with the molten silicon,and a single crystal is grown by slow extraction. After formation of aneck is complete, the diameter of the crystal is enlarged by, forexample, decreasing the pulling rate and/or the melt temperature untilthe desired or target diameter is reached. The cylindrical main body ofthe crystal which has an approximately constant diameter is then grownby controlling the pull rate and the melt temperature while compensatingfor the decreasing melt level. Near the end of the growth process butbefore the crucible is emptied of molten silicon, the crystal diameteris typically reduced gradually to form a tail end in the form of anend-cone. The end-cone usually is formed by increasing the crystal pullrate and heat supplied to the crucible. When the diameter becomes smallenough, the crystal is then separated from the melt.

Czochralski growing techniques include the batch Czochralski method andthe continuous Czochralski method. In batch CZ, a single polycrystallinecharge is loaded into the crucible, the single charge being sufficientto grow a single crystal silicon ingot, after which the crucible isessentially depleted of silicon melt. In continuous Czochralski (CCZ)growth, polycrystalline silicon may be continually or periodically addedto the molten silicon to replenish the melt during the growth processand, as a result, multiple ingots can be pulled from a single crucibleduring a growth process.

To carry out the CCZ process, the traditional batch Czochralski growthchamber and apparatus are modified to include a means for feedingadditional polycrystalline silicon to the melt in a continuous orsemi-continuous fashion without adversely affecting the properties ofthe growing ingot. As the seed crystal is continuously grown from themelt, solid polycrystalline silicon such as granular polycrystallinesilicon is added to the melt to replenish the melt. The feed rate of theadditional solid polycrystalline silicon added to the melt is typicallycontrolled to maintain process parameters. In order to reduce theadverse effects of this replenishing activity on simultaneous crystalgrowth, the traditional quartz crucible is often modified to provide anouter or annular melt zone into which the added material is deliveredalong with an inner growth zone from which the silicon ingot is pulled.These zones are in fluid flow communication with one another.

The continuously shrinking size of the modern microelectronic deviceimposes challenging restrictions on the quality of the siliconsubstrate, which is essentially determined by the size and thedistribution of the grown-in microdefects. Most of the microdefectsformed in silicon crystals grown by the Czochralski (CZ) process and theFloat Zone (FZ) process are the agglomerates of intrinsic point defectsof silicon—vacancies and self-interstitials (or, simply, interstitials).

A series of studies have established that the interstitial agglomeratesexist in two forms—globular interstitial clusters, termed B swirl defect(or B-defects), and the dislocation loops, termed A swirl defect (orA-defects). Later discovered vacancy agglomerates, known as D-defects,have been identified as octahedral voids. Voronkov provided thewell-accepted explanation for the microdefect distributions observed insilicon crystals on the basis of the crystal growth conditions.According to Voronkov's model, or theory, the temperature field in thevicinity of the melt/crystal interface drives the recombination of thepoint defects providing driving forces for their diffusion from themelt/crystal interface—where they exist at their respective equilibriumconcentrations—into the crystal bulk. The interplay between thetransport of the point defects, both by the diffusion and theconvection, and their recombination establishes the point defectconcentration beyond a short distance away from the interface, termedthe recombination length. Typically, the difference between the vacancyconcentration and the interstitial concentration beyond therecombination length, termed the excess point defect concentration,remains essentially fixed away from the lateral surface of the crystal.In a rapidly pulled crystal, the spatial redistribution of the pointdefects by their diffusion beyond the recombination length is generallynot important—with the exception of a region close to the lateralsurface of the crystal that acts as a sink or a source of the pointdefects. Therefore, if the excess point defect concentration beyond therecombination length is positive, vacancies remain in excess, andagglomerate to form D-defects at lower temperatures. If the excess pointdefect concentration is negative, interstitials remain the dominantpoint defects, and agglomerate to form A-defects and B-defects. If theexcess point defect concentration is below some detection threshold, nodetectable microdefects are formed. Thus, typically, the type ofgrown-in microdefects is determined simply by the excess point defectconcentration established beyond the recombination length. The processof establishing the excess point defect concentration is termed theinitial incorporation and the dominant point defect species is termedthe incorporated dominant point defect. The type of the incorporatedpoint defects is determined by the ratio of the crystal pull-rate (v) tothe magnitude of the axial temperature gradient in the vicinity of theinterface (G). At a higher v/G, the convection of the point defectsdominates their diffusion, and vacancies remain the incorporateddominant point defects, as the vacancy concentration at the interface ishigher than the interstitial concentration. At a lower v/G, thediffusion dominates the convection, allowing the incorporation of thefast diffusing interstitials as the dominant point points. At a v/Gclose to its critical value, both the point defects are incorporated invery low and comparable concentrations, mutually annihilating each otherand thus suppressing the potential formation of any microdefects atlower temperatures. The observed spatial microdefect distribution can betypically explained by the variation of v/G, caused by a radialnon-uniformity of G and by an axial variation of v. A striking featureof the radial microdefect distribution is the oxide particles formedthrough the interaction of oxygen with vacancies in the regions ofrelatively lower incorporated vacancy concentration—at a small range ofv/G marginally above the critical v/G. These particles form a narrowspatial band that can be revealed by thermal oxidation as the OSF(oxidation-induced stacking faults) ring. Quite often, the OSF ringmarks the boundary between adjacent crystal regions that arevacancy-dominated and interstitial-dominated, known as the V/I boundary.

The microdefect distributions in CZ crystals grown at lower rates inmany modern processes, however, are influenced by the diffusion of thepoint defects in the crystal bulk, including the diffusion induced bythe lateral surfaces of the crystals. Therefore, an accuratequantification of the microdefect distributions in CZ crystalspreferably incorporates the 2-dimensional point defect diffusion, bothaxially and radially. Quantifying only the point defect concentrationfield can qualitatively capture the microdefect distribution in a CZcrystal, as the type of the microdefects formed is directly determinedby it. For a more accurate quantification of the microdefectdistribution, however, capturing the agglomeration of the point defectsis necessary. Traditionally, the microdefect distribution is quantifiedby decoupling the initial incorporation of the point defects and thesubsequent formation of the microdefects. This approach ignores thediffusion of the dominant point defects in the vicinity of thenucleation region, from the regions at higher temperatures (where themicrodefect density is negligible) to the regions at lower temperatures(where the microdefects exist in higher densities and consume the pointdefects). Alternatively, a rigorous numerical simulation based onpredicting the size distributions of the microdefect populations atevery location in the crystal is numerically expensive.

The transition between vacancy and interstitial dominated materialoccurs at a critical value of v/G, which currently appears to be about2.5×10⁻⁵ cm²/sK. If the value of v/G exceeds the critical value,vacancies are the predominant intrinsic point defect, with theirconcentration increasing with increasing v/G. If the value of v/G isless than the critical value, silicon self-interstitials are thepredominant intrinsic point defect, with their concentration increasingwith decreasing v/G. Accordingly, process conditions, such as growthrate (which affect v), as well as hot zone configurations (which affectG), can be controlled to determine whether the intrinsic point defectswithin the single crystal silicon will be predominantly vacancies (wherev/G is generally greater than the critical value) or self-interstitials(where v/G is generally less than the critical value).

Agglomerated defect formation generally occurs in two steps. First,defect “nucleation” occurs, which is the result of the intrinsic pointdefects being supersaturated at a given temperature; above this“nucleation threshold” temperature, intrinsic point defects remainsoluble in the silicon lattice. The nucleation temperature foragglomerated intrinsic point defects is greater than about 1000° C.

Once this “nucleation threshold” temperature is reached, intrinsic pointdefects agglomerate; that is, precipitation of these point defects outof the “solid solution” of the silicon lattice occurs. The intrinsicpoint defects will continue to diffuse through the silicon lattice aslong as the temperature of the portion of the ingot in which they arepresent remains above a second threshold temperature (i.e., a“diffusivity threshold”). Below this “diffusivity threshold”temperature, intrinsic point defects are no longer mobile withincommercially practical periods of time.

While the ingot remains above the “diffusivity threshold” temperature,vacancy or interstitial intrinsic point defects diffuse through thesilicon lattice to sites where agglomerated vacancy defects orinterstitial defects, respectively, are already present, causing a givenagglomerated defect to grow in size. Growth occurs because theseagglomerated defect sites essentially act as “sinks,” attracting andcollecting intrinsic point defects because of the more favorable energystate of the agglomeration.

Vacancy-type defects are recognized to be the origin of such observablecrystal defects as D-defects, Flow Pattern Defects (FPDs), Gate OxideIntegrity (GOI) Defects, Crystal Originated Particle (COP) Defects,crystal originated Light Point Defects (LPDs), as well as certainclasses of bulk defects observed by infrared light scattering techniquessuch as Scanning Infrared Microscopy and Laser Scanning Tomography. Alsopresent in regions of excess vacancies are clusters of oxygen or silicondioxide. Some of these clusters remain small and relatively strain-free,causing essentially no harm to a majority of devices prepared from suchsilicon. Some of these clusters are large enough to act as the nucleifor ring oxidation induced stacking faults (OISF). It is speculated thatthis particular defect is facilitated by previously nucleated oxygenagglomerates catalyzed by the presence of excess vacancies. The oxideclusters are primarily formed in CZ growth below 1000° C. in thepresence of moderate vacancy concentration.

Defects relating to self-interstitials are less well studied. They aregenerally regarded as being low densities of interstitial-typedislocation loops or networks. Such defects are not responsible for gateoxide integrity failures, an important wafer performance criterion, butthey are widely recognized to be the cause of other types of devicefailures usually associated with current leakage problems.

In this regard it is to be noted that, generally speaking, oxygen ininterstitial form in the silicon lattice is typically considered to be apoint defect of silicon, but not an intrinsic point defect, whereassilicon lattice vacancies and silicon self-interstitials (or, simply,interstitials) are typically considered to be intrinsic point defects.Accordingly, essentially all microdefects may be generally described asagglomerated point defects, while D-defects (or voids), as well asA-defects and B-defects (i.e., interstitial defects) may be morespecifically described as agglomerated intrinsic point defects. Oxygenclusters are formed by absorbing vacancies; hence, oxygen clusters canbe regarded as agglomerates of both vacancies and oxygen.

It is to be further noted that the density of such vacancy andself-interstitial agglomerated point defects in Czochralski siliconhistorically has been within the range of about 1×10³/cm³ to about1×10⁷/cm³, whereas the density of oxygen clusters varies between around1×10⁸/cm³ to 1×10¹⁰/cm³. Agglomerated intrinsic point defects aretherefore of rapidly increasing importance to device manufacturers,because such defects can severely impact the yield potential of thesingle crystal silicon material in the production of complex and highlyintegrated circuits.

In view of the foregoing, in many applications it is preferred that aportion or all of the silicon crystal, which is subsequently sliced intosilicon wafers, be substantially free of these agglomerated intrinsicpoint defects. To-date, several approaches for growing substantiallydefect-free silicon crystals have been reported. Generally speaking, allthese approaches involve controlling the ratio v/G, in order todetermine the initial type and concentration of intrinsic point defectspresent in the growing CZ single crystal silicon crystal. Additionally,however, such approaches may involve controlling the subsequent thermalhistory of the crystal to allow for prolonged diffusion time to suppressthe concentration of intrinsic point defects therein, and thussubstantially limit or avoid the formation of agglomerated intrinsicpoint defects in a portion or all of the crystal. (See, for example,U.S. Pat. Nos. 6,287,380; 6,254,672; 5,919,302; 6,312,516 and 6,328,795;the entire contents of which are hereby incorporated herein byreference.) Alternatively, however, such approaches may involve arapidly cooled silicon (RCS) growth process, wherein the subsequentthermal history of the crystal is then controlled to rapidly cool atleast a portion of the crystal through a target nucleation temperature,in order to control the formation of agglomerated intrinsic pointdefects in that portion. One or both of these approaches may alsoinclude allowing at least a portion of the grown crystal to remain abovethe nucleation temperature for a prolonged period of time, to reduce theconcentration of intrinsic point defects prior to rapidly cooling thisportion of the crystal through the target nucleation temperature, thussubstantially limiting or avoiding the formation of agglomeratedintrinsic point defects therein. (See, e.g., U.S. Patent ApplicationPublication No. 2003/0196587, the entire disclosure of which isincorporated herein by reference.) Still further, methods have beendeveloped to reduce or eliminate agglomerated point defects from thecenter of the ingot to the edge by the simultaneous control of thecooling rate of the solidified ingot and the radial variation of theaxial temperature gradient in the vicinity of the interface (G). (See,e.g., U.S. Pat. No. 8,673,248, the entire disclosure of which isincorporated herein by reference.)

Polished silicon wafers that meet manufacturer requirements for lack ofagglomerated point defects, e.g., crystal originated pits (COP), may bereferred to as Neutral Silicon or Perfect Silicon. Perfect Siliconwafers are preferred for many semiconductor applications as a lower costpolished wafer alternative to, for example, higher epitaxially depositedwafers. In the course of the last 20 years, many silicon wafer suppliershave developed Defect Free and COP Free wafer products in both 200 mmand 300 mm diameter for sale mostly to the Memory (DRAM/NAND/FLASH)market which traditionally has been more sensitive to cost pressureswithin the market. The industrial standard for acceptable defectivityhas evolved over this time frame in terms of acceptable level of lightpoint scatterings (LLS) and Gate Oxide Intensity (GOI) as customerapplications device nodes have shrunk. For example, an industrial COPfree specification may have been, at one time, less than a few hundredat no more than 0.12 μm size. More current standards demand less than 20COPs at no more than 0.026 μm size to qualify as perfect silicon. Asanother example, the past standard for GOI in a MOS transistor was 95%at 8MV (B-mode). Currently, specifications are moving to 99% at 10˜12MV(D-mode). On top of this requirement, the need for improved radialoxygen precipitation across the wafer as measured traditionally by BMDdensity (bulk micro defects) and BMD size distribution are required asdevice nodes shrink in order to avoid substrate slip during processingor warp that may impact patterned overlay during device lithography. Asthese specifications have tightened (LLS, GOI, BMD uniformity, etc.),the control window for defect and COP free silicon growth has shrunkconsiderably, reducing crystal throughput of the process considerably.This is because the window of acceptable band structure (which can bedirectly translated to process window of operation) has shifted overtime with the specifications.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the disclosure, which aredescribed and/or claimed below. This discussion is believed to behelpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

SUMMARY

One aspect of the present disclosure is directed to a method ofpreparing a single crystal silicon ingot by the Continuous Czochralskimethod, the method comprising: adding an initial charge ofpolycrystalline silicon to a crucible, the initial charge furthercomprising a source of nitrogen; heating the crucible comprising theinitial charge of polycrystalline silicon and the source of nitrogen tocause a silicon melt to form in the crucible, the silicon meltcomprising an initial volume of molten silicon and having an initialmelt elevation level; contacting a silicon seed crystal with a siliconmelt; withdrawing the silicon seed crystal to grow a neck portion,wherein the silicon seed crystal is withdrawn at a neck portion pullrate during growth of the neck portion, and further wherein the neckportion has a neck portion nitrogen concentration of at least about1×10¹³ atoms/cm³; withdrawing the silicon seed crystal to grow anoutwardly flaring seed-cone adjacent the neck portion, wherein thesilicon seed crystal is withdrawn at a seed-cone pull rate during growthof the outwardly flaring seed-cone, and further wherein the outwardlyflaring seed-cone has an outwardly flaring seed-cone nitrogenconcentration of at least about 1×10¹³ atoms/cm³; and withdrawing thesilicon seed crystal to grow a main body of the single crystal siliconingot adjacent the outwardly flaring seed-cone, wherein the silicon meltcomprises a volume of molten silicon and a melt elevation level duringgrowth of the main body of the single crystal silicon ingot, and furtherwherein the main body of the single crystal silicon has a main bodynitrogen concentration of at least about 1×10¹³ atoms/cm³; wherein themain body of the single crystal silicon ingot is grown at an initialvariable main body pull rate and a constant main body pull rate, whereinthe main body of the single crystal silicon ingot is grown at theinitial variable main body pull rate for less than about 20% of a lengthof the main body of the single crystal silicon ingot and grown at theconstant main body pull rate during growth for at least about 30% of thelength of the main body of the single crystal silicon ingot; and furtherwherein polycrystalline is continuously fed or periodically feed to thecrucible to thereby replenish a volume of molten silicon and to therebymaintain a melt elevation level in the crucible during growth of themain body of the single crystal silicon ingot and the source of nitrogenis continuously fed or periodically fed to the crucible to therebyreplenish an amount of nitrogen.

In another aspect, the present disclosure is directed to a singlecrystal silicon ingot having a main body portion, wherein the main bodyportion has a circumferential edge, a central axis having an axiallength that is parallel to the circumferential edge, and a radius thatextends from the central axis to the circumferential edge, wherein awafer sliced from any portion of the main body over at least 60% ofaxial length of the main body of the single crystal silicon ingot, atleast 70% of axial length of the main body of the single crystal siliconingot, or at least 80% of axial length of the main body of the singlecrystal silicon ingot is characterized by non-detectable FPDs (FlowPattern Defect by Secco etching technique) and DSODs (Direct SurfaceOxide Defect particle count after electric breakdown) and zero I-defects(A-defect) by Secco-etching technique.

In another aspect, the present disclosure is directed to a singlecrystal silicon ingot having a main body portion, wherein the main bodyportion has a circumferential edge, a central axis having an axiallength that is parallel to the circumferential edge, and a radius thatextends from the central axis to the circumferential edge, wherein themain body portion comprises: interstitial oxygen at a main body oxygenconcentration that varies by no more than 20% above and no less than 20%below an average main body oxygen concentration over at least 40% ofaxial length of the main body of the single crystal silicon ingot, atleast 50% of axial length of the main body of the single crystal siliconingot, at least 60% of axial length of the main body of the singlecrystal silicon ingot, at least 70% of axial length of the main body ofthe single crystal silicon ingot, or at least 80% of axial length of themain body of the single crystal silicon ingot.

In another aspect, the present disclosure is directed to a singlecrystal silicon ingot having a main body portion, wherein the main bodyportion has a circumferential edge, a central axis having an axiallength that is parallel to the circumferential edge, and a radius thatextends from the central axis to the circumferential edge, wherein themain body portion comprises: nitrogen at a main body nitrogenconcentration that varies by no more than 20% above and no less than 20%below an average main body nitrogen concentration over at least 40% ofaxial length of the main body of the single crystal silicon ingot, atleast 50% of axial length of the main body of the single crystal siliconingot, at least 60% of axial length of the main body of the singlecrystal silicon ingot, at least 70% of axial length of the main body ofthe single crystal silicon ingot, or at least 80% of axial length of themain body of the single crystal silicon ingot.

In another aspect, the present disclosure is directed to a singlecrystal silicon ingot having a main body portion, wherein the main bodyportion has a circumferential edge, a central axis having an axiallength that is parallel to the circumferential edge, and a radius thatextends from the central axis to the circumferential edge, wherein themain body portion comprises: further wherein the main body portion has aresistivity that varies by no more than 20% above and no less than 20%below an average main body resistivity over at least 40% of axial lengthof the main body of the single crystal silicon ingot, at least 50% ofaxial length of the main body of the single crystal silicon ingot, atleast 60% of axial length of the main body of the single crystal siliconingot, at least 70% of axial length of the main body of the singlecrystal silicon ingot, or at least 80% of axial length of the main bodyof the single crystal silicon ingot.

Various refinements exist of the features noted in relation to theabove-mentioned aspects of the present disclosure. Further features mayalso be incorporated in the above-mentioned aspects of the presentdisclosure as well. These refinements and additional features may existindividually or in any combination. For instance, various featuresdiscussed below in relation to any of the illustrated embodiments of thepresent disclosure may be incorporated into any of the above-describedaspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A (early body growth), 1B (middle body growth), and 1C (late bodygrowth) illustrate the melt volume or depth and crucible position as afunction of crystal length during an exemplary batch Czochralskiprocess.

FIG. 2A is a graph depicting the constant change in pull rate requiredto achieve sufficient defectivity control in an ingot grown by anexemplary batch Cz process.

FIG. 2B is a graph depicting the change in nitrogen dopant concentrationdue to the segregation coefficient effect in an ingot grown by anexemplary batch Cz process.

FIG. 3 is a graph depicting the pull rate profile required to achievesufficient defectivity control in an ingot grown by an exemplary batchCz process with an applied magnetic field.

FIG. 4A is a graph depicting the pull rate profile required to achievesufficient defectivity control in an ingot grown by an exemplarycontinuous Cz process according to the method of the present disclosure.

FIG. 4B is a graph comparing the nitrogen dopant concentration betweenan ingot grown by an exemplary batch Cz process and in an ingot grown byan exemplary continuous Cz process according to the method of thepresent disclosure.

FIG. 5 depicts an exemplary crucible configuration suitable for anexemplary continuous Cz process according to the method of the presentdisclosure.

FIGS. 6A, 6B, and 6C illustrate the melt level and ingot growth anexemplary continuous Cz process according to the method of the presentdisclosure.

FIG. 7 is a graph depicting a nitrogen source addition protocol into amelt to grow an ingot grown by an exemplary continuous Cz processaccording to the method of the present disclosure.

FIGS. 8A and 8B illustrate magnetic fields applied to the silicon meltduring growth of an ingot by an exemplary continuous Cz processaccording to the method of the present disclosure.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

In the context of the present disclosure, “perfect silicon” refers toCzochralski grown single crystal silicon ingots or single crystalsilicon wafers sliced from Czochralski grown single crystal siliconingots grown under conditions to meet or exceed the standards of PerfectSilicon™ (SunEdison Semiconductor, Ltd.). These standards include aningot or wafer sliced therefrom that meets or exceeds industryspecifications for agglomerated defects, DSOD (direct surface oxidedefects), COP (crystal originated pits or particles), D-Defects, andI-defects, etc. For example, “perfect silicon” wafers may becharacterized by non-detectable FPD (Flow Pattern Defect by Seccoetching technique) and DSOD (Direct Surface Oxide Defect particle countafter electric breakdown) and zero I-defect (A-defect) by Secco-etchingtechnique. The Secco etch comprises applying a dilute aqueous solutionof an alkali dichromate and hydrofluoric acid, for suitably revealingdislocations and other lattice defects in the various crystallographic(100), (111), and (110) planes of silicon. The etch brings out bothlineage (low angle grain boundaries) and slip lines. The method of thepresent disclosure enables the growth of a single crystal silicon ingotcomprising perfect silicon, e.g., wafers sliced from such an ingot, overat least about 70% of the length of the main body of the single crystalsilicon ingot, such as over at least about 80% of the length of the mainbody of the single crystal silicon ingot, or even over at least about90% of the length of the main body of the single crystal silicon ingot.In some embodiments, wafers sliced from ingots grown over at least about60% of the length of the main body of the single crystal silicon ingot,over at least about 70% of the length of the main body of the singlecrystal silicon ingot, such as over at least about 80% of the length ofthe main body of the single crystal silicon ingot, or even over at leastabout 90% of the length of the main body of the single crystal siliconingot are characterized by non-detectable FPD (Flow Pattern Defect bySecco etching technique) and DSOD (Direct Surface Oxide Defect particlecount after electric breakdown) and zero I-defect (A-defect) bySecco-etching technique. In some embodiments, wafers sliced from ingotsgrown over at least about 60% of the length of the main body of thesingle crystal silicon ingot, over at least about 70% of the length ofthe main body of the single crystal silicon ingot, such as over at leastabout 80% of the length of the main body of the single crystal siliconingot, or even over at least about 90% of the length of the main body ofthe single crystal silicon ingot are characterized by GOI yield (i.e.,non-failure) in a MOS transistor at 95% or more, preferably 99% or more,at ≥8MV (B-mode), and/or 95% or more, preferably 99% or more, at 10˜12MV(D-mode). In some embodiments, wafers sliced from ingots over at leastabout 60% of the length of the main body of the single crystal siliconingot, grown over at least about 70% of the length of the main body ofthe single crystal silicon ingot, such as over at least about 80% of thelength of the main body of the single crystal silicon ingot, or evenover at least about 90% of the length of the main body of the singlecrystal silicon ingot by less than 20 COPs at no more than 0.026 μm sizeto qualify as perfect silicon.

In a conventional batch Czochralski process to grow a single crystalsilicon ingot, the crystal melt/interface and the thermal condition bothvary continuously as a function of increasing ingot length due to theconsumption of silicon melt during ingot growth and variability of thecrucible position. A depiction of the melt depletion and the movement ofthe crucible may be found in FIG. 1. FIGS. 1A (early body growth), 1B(middle body growth), and 1C (late body growth) illustrate the meltlevel and crucible height as a function of crystal length during a batchCz process. Since the melt conditions, e.g., mass and elevation levels,and the crucible location are continuously changing during a batchprocess, the v/G ratio (growth rate V/axial temperature gradient G)necessary to minimize defectivity is continuously changing over crystallength, shifting the quality of the crystal. In order to maintain thedesired quality to meet specification within the process window,continuous control adjustment of several parameters is required byposition. These parameters include crucible rotation rate (C/R), seedrotation rate (S/R), seed lift rate (S/L), heater power, reflectorheight, etc. See FIG. 2A, which is a graph depicting the constant changein pull rate required to achieve sufficient defectivity control in aningot grown by an exemplary batch Cz process. The line defined by thetriangle (---▴---) is the constantly changing critical pull rate toachieve the critical v/G value. The pull rate may vary within the uppercritical pull rate (“UCL”) marked by the square (---▪---) and the lowercritical pull rate (“LCL”) marked by the diamond (---♦---) and stillachieve acceptable defectivity control. These three lines indicate thepull speed that can produce perfect silicon. Within the upper and lowerpull speed boundaries, perfect silicon may be produced having varyingdominant intrinsic point defects. For example, vacancy dominant (“Pv”)silicon is produced when the applied pull speed is controlled betweenthe lines labelled with the Triangle and square in FIG. 2A (and FIGS. 3and 4), and interstitial dominant (“Pi”) silicon is produced when theapplied pull speed is controlled between the lines labeled with theTriangle and diamond in FIG. 2A (and FIGS. 3 and 4). In the exampledepicted in FIG. 2A (and FIGS. 3 and 4), early and middle portions ofingot growth, perfect silicon having vacancy dominant point defects maybe grown, as shown by the representation of the ingot cross sectionlabeled “Pv.” FIG. 2A depicts that the ingot is vacancy dominant fromcenter to edge. In the example depicted in FIG. 2A, in later growth, theingot is characterized by regions of vacancy dominant point defects andinterstitial dominant point defects, which is represented in the crosssection regions labeled “Pi.” For example, an ingot may be grown that isinterstitial dominant from center to a radial length less than theradius of the entire ingot, which is surrounded by a band of vacancydominant material to the edge of the ingot. In a still later region, thecross section of the ingot shows vacancy dominant material in thecenter, surrounded by a band of interstitial dominant material,surrounded by another band of vacancy dominant material at the edge.These depictions are merely for illustration and are not intended to belimiting upon the method of the present disclosure. Perfect Silicon,i.e., ingots and wafers sliced therefrom that are free of detectableagglomerated point defects, results from the proper control of excesspoint defects (vacancy and interstitial silicon) in part by the pullrate of the ingot. Intrinsic point defects, such as vacancies andinterstitials, occur in ingots grown by the Czocrhalski method. Presenceof such defects has no impact on whether the silicon is perfect. Rather,perfect silicon is characterized as being free of agglomerated pointdefects, such as COPs, DSODs, and I-defects.

FIG. 2A (and also FIGS. 3 and 4A) also indicate the agglomerated defectswhich may result in the ingot as a function of pull speeds outside theupper and lower limits of critical v/G at any crystal length. Thedefects which may occur if the upper critical pull rate is exceeded (v/Gis higher than a critical v/G) include DSOD (direct surface oxidedefects) or COP (crystal originated pits or particles). Defects whichmay occur if the pull rate is below the lower critical pull rate (v/G islower than a critical v/G) include I-defects. The bands in which thesedefects occur are also shown in the ingot cross sections. In regionswherein the dominant excess point defect is vacancies, agglomerations ofvacancy defects form bulky defect such as COP, DSOD by agglomeration andprecipitation of vacancies during the Cz silicon crystal growth andcooling. In regions wherein the dominant excess point defect is theinterstitial silicon atoms, they agglomerate to form bulk defect such asI-defect by agglomeration/precipitation of interstitial silicon andpunch out the dislocation. Any small deviation of v/G will form a defectby agglomeration of either vacancy or interstitial silicon atom.

In addition to substrate defectivity control, wafer strength is anotherimportant variable for certain applications, such as FLASH devices, inwhich higher wafer strength is advantageous due to vertical stacking ofdevices. In some techniques, wafer strength is provided by oxygenprecipitation and manipulation of intrinsic gettering. For example,increasing oxygen content in the wafer is a predominant way tomanipulate oxygen precipitation. In addition to oxygen contentmanipulation or instead of, the melt and the ingot grown therefrom maybe doped with impurities such as nitrogen, which may manipulate both COPsize and BMD density. Nitrogen doping may also provide a larger perfectsilicon quality window vs. non-Nitrogen doped material. Nitrogen dopingmay segregate axially during growth due to a segregation coefficienteffect. The nitrogen segregation coefficient is below unity and has beenreported to be about 7×10⁻⁴. Accordingly, nitrogen does notpreferentially partition into the ingot during growth, which causes thenitrogen content in the melt to increase during the ingot pullingprocess, which thereby increases the nitrogen content along the axiallength of the growing single crystal silicon ingot. See FIG. 2B, whichis a graph depicting the increase of nitrogen concentration, which maybe as much as 7× or more from the beginning of ingot growth to the endof ingot growth, that may occur along the axial length of a crystalprepared according to a batch Czochralski method with melt conditions asdepicted in FIGS. 1A through 1C and process conditions as depicted inFIG. 2A. Nitrogen axial variation and changing crystal/melt interfaceand thermal conditions due to the change of crystal position duringgrowth as poly Silicon is consumed (see FIGS. 1A through 1C) arebarriers to maintaining good PS quality axially unless they arecompensated for during growth through constant tuning of the crystalgrowth conditions. Because of this, v/G is continuously changing overcrystal length, which may thereby shift the quality of the crystal.

Magnetic fields, e.g., horizontal or cusp, may be applied to alter themelt flow pattern within the crucible and enable enhanced control of theshape and height of the crystal/melt interface, which thereby enhancesquality control. However, pull rates and other parameters must still bevaried to achieve acceptable defectivity control, as exemplified in FIG.3. FIG. 3 is a graph depicting the pull rate profiles required toachieve sufficient defectivity control in an ingot grown by an exemplarybatch Cz process with an applied magnetic field. The line defined by thetriangle (---▴---) is the critical pull rate to achieve the critical v/Gvalue, which varies continuously during growth of the single crystalsilicon ingot, as necessary. The pull rate may vary within the uppercritical pull rate (“UCL”) marked by the square (---▪---) and the lowercritical pull rate (“LCL”) marked by the diamond (---♦---) and stillachieve acceptable defectivity control. The regions of intrinsic pointdefect and agglomerated point defect in the cross section of the singlecrystal silicon ingot are substantially as described above in thedescription of FIG. 2A.

According to the method of the present disclosure, a single crystalsilicon ingot is grown by the continuous Czochralski (CCZ) method underconditions that enable the melt depth (i.e., elevation level of themolten silicon) and thermal conditions to remain substantially constantduring growth because melt is continuously replenished as it isconsumed. In some embodiments, maintaining a substantially constantelevation level of the molten silicon enables maintaining the cruciblein a fixed position. Once v/G is fixed with the appropriate hot zoneconfiguration, the process window will be fixed (i.e., no controladjustment) over a substantial portion of the crystal length. Once theprocess conditions (S/R, power, gas flow and pressure, magnetic fluxdensity, Cusp or HMCZ MGP position) are set, gas flow and/or chamberpressure and C/R are used to control oxygen content. Accordingly, themethod of the present disclosure enables growth of a single crystalsilicon ingot by the continuous Czochralski (CCZ) method in which thepull speed is constant during growth of a substantial length of theingot, and the grown ingot according to this method has uniform andacceptable defectivity control, Oi uniformity, BMD uniformity, andnitrogen content uniformity over a substantial portion of the axiallength of the ingot.

After all conditions are set to steady state, the pull rate to produce asingle crystal silicon ingot having the desired defectivity control inthe entire crystal length will be constant, significantly reducingquality losses in production due to process control as compared toconventional Cz process. FIG. 4A is a graph of the pull rate as afunction of axial length of the single crystal silicon ingot during anexemplary continuous Czochralski growth method according to the presentdisclosure. As shown in FIG. 4A, a constant pull rate is maintained overa substantial portion of the growth of the main body portion of thesingle crystal silicon ingot. The line defined by the triangle (---▴---)is the critical pull rate to achieve the critical v/G value, which hasan initial varying region, followed by a region of constant pull rateover a substantial portion of the growth of the main body portion of thesingle crystal silicon ingot. The pull rate may vary within the uppercritical pull rate (“UCL”) marked by the square (---▪---) and the lowercritical pull rate (“LCL”) marked by the diamond (---♦---) and stillachieve acceptable defectivity control. The regions of intrinsic pointdefect and agglomerated point defect in the cross section of the singlecrystal silicon ingot are substantially as described above in thedescription of FIG. 2A.

In the CCZ process according to the method of the present disclosure,polycrystalline silicon feeding is continuous with the crystal growth,thereby the melt volume is maintained substantially the same as theinitial charge melt depth regardless of crystal length. Since meltelevation is controlled by the mass balance between the growing crystalweight and the continuously fed polycrystalline silicon, the thermalcondition in the melt and growing crystal is unchanged throughout theaxial growth. Subsequently, once the desired crystal/melt interface isdetermined and fixed by parameters such as magnetic field, C/R and S/R,pull rate, heater power, etc., defect quality and Oi control will bemaintained constant throughout the crystal axial growth. Further,because the thermal conditions and crystal/melt interface are fixedduring the crystal growth, a constant pull rate for a given HZ andcrystal/melt interface can be used over the entire crystal length in aquasi-steady state control.

According to the method of the present disclosure, the thermal conditionsuitable for achieving growth of the single crystal silicon ingotmeeting the requirements for defectivity control is set by the hot zoneconfiguration. The growth method is the continuous Czochralski method.Accordingly, the furnace chamber comprises means, e.g., a feeding tube,for continuous feeding of polycrystalline silicon. The solid polysiliconadded to the crucible is typically granular polysilicon, although chunkpoly silicon may be used, and it is fed into the crucible using apolysilicon feeder that is optimized for use with granular polysilicon.Chunk polysilicon typically has a size of between 3 and 45 millimeters(e.g., the largest dimension), and granular polysilicon typically has asize between 400 and 1400 microns. Granular polysilicon has severaladvantages including providing for easy and precise control of the feedrate due to the smaller size. However, the cost of granular polysiliconis typically higher than that of chunk polysilicon due to the chemicalvapor deposition process or other manufacturing methods used in itsproduction. Chunk polysilicon has the advantage of being cheaper andbeing capable of a higher feed rate given its larger size. The locationof the heating units, cooling jacket, and operation of the power controlare adjusted to accommodate the polycrystalline silicon feeder.

A depiction of a crucible 10 having a plurality of weirs (20, 30, 40) orfluid barriers that separate the melt into different melt zones is shownin FIG. 5. In the illustrated embodiment, the crucible assembly 10includes a first weir 20 (broadly, a fluid barrier) defining the innermelt zone 22 of the silicon melt. The inner melt zone 22 is the growthregion from which the single crystal silicon ingot 50 is grown. A secondweir 30 defines a middle melt zone 32 of the silicon melt. Finally, athird weir 40 defines an outer melt zone 42 of the silicon melt. Afeeding tube (not shown) feeds polycrystalline silicon, which may begranular, chunk, or a combination of granular and chunk, into the outermelt zone 42 at a rate sufficient to maintain a substantially constantmelt elevation level and volume during growth of the ingot. The firstweir 20, second weir 30, and third weir 40 each have a generally annularshape, and have at least one opening defined therein to permit moltensilicon to flow radially inward towards the growth region of the innermelt zone 22. The crucible configuration depicted in FIG. 5 is exemplaryand suitable for carrying out the process of the present disclosure.Other configurations suitable for CCZ may be used without departing fromthe scope of the present disclosure. For example, the crucible 10 maylack the second weir 30 and/or may lack the third weir 40.

Generally, the melt from which the ingot is drawn is formed by loadingpolycrystalline silicon into a crucible to form an initial siliconcharge. In general, an initial charge is between about 100 kilograms andabout 400 kilograms of polycrystalline silicon, such as between about100 kilograms and about 300 kilograms of polycrystalline silicon, orbetween about 100 kilograms and about 200 kilograms of polycrystallinesilicon, which may be granular, chunk, or a combination of granular andchunk. The mass of the initial charges depends on the desired crystaldiameter and HZ design. Initial charge does not reflect the length ofcrystal, because polycrystalline silicon is continuously fed duringcrystal growth. For example, if polycrystalline silicon is fedcontinuously and the chamber height is tall enough, crystal length canbe extended to 2000 mm, 3000 mm, or even 4000 mm in length. The cruciblemay have the configuration depicted in FIG. 5, or another configurationsuitable for CCZ growth. A variety of sources of polycrystalline siliconmay be used including, for example, granular polycrystalline siliconproduced by thermal decomposition of silane or a halosilane in afluidized bed reactor or polycrystalline silicon produced in a Siemensreactor.

In some embodiments, the melt is further charged with a source ofnitrogen so that the single crystal silicon ingot grown according to themethod of the present disclosure is doped with nitrogen. In someembodiments, the source of nitrogen is a solid source of nitrogen, suchas silicon nitride. Silicon nitride may have the chemical formulaSi_(X)N_(Y), wherein X and Y are both 1 or one or both of X and Y aremore than 1. Any form of silicon nitride may be used, with Si₃N₄ beingthe most common and stable. The silicon nitride may be granular or inthe form of a powder. In some embodiments, the source of nitrogen is asilicon wafer having a silicon nitride film on a surface thereof. Thesilicon nitride film may be deposited on the silicon wafer by chemicalvapor deposition to deposit, for example, a 0.5 to 10 micrometer thickfilm, such as about 1 micrometer thick film, on one or both sides of thewafer. The silicon wafer may be added whole or it may be crushed intosmall pieces. In some embodiments, the source of nitrogen is siliconoxynitride glass. In some embodiments, nitrogen doping may beaccomplished by doping with a nitrogen containing gas, such as nitrogen(N₂) gas. To form the initial charge, the source of nitrogen, if a solidsource is used, may be added directly to the polycrystalline siliconcharge. As the single crystal silicon ingot is grown, the source ofnitrogen is added, periodically or continuously, to maintain a uniformconcentration of nitrogen in each portion of the single crystal siliconingot.

The method of the present disclosure enables a uniform nitrogenconcentration in each portion of the growing single crystal siliconingot, including the neck portion, the outwardly flaring seed coneportion, and the main body of the single crystal silicon ingot. In someembodiments, the nitrogen concentration in each portion of the growingsingle crystal silicon ingot is at least about 1×10¹³ atoms/cm³, such asbetween about 1×10¹³ atoms/cm³ and about 1×10¹⁵ atoms/cm³, or betweenabout 1×10¹³ atoms/cm³ and about 1.5×10¹⁴ atoms/cm³, or between about5×10¹³ atoms/cm³ and about 1×10¹⁴ atoms/cm³. Preferably, the variationof the nitrogen concentration is not more than about 20% more than andnot less than 20% less than the set point or average nitrogenconcentration over the axial length of the single crystal silicon ingot.More preferably, the variation of the nitrogen concentration is not morethan about 10% more than and not less than 10% less than the set pointor average nitrogen concentration over the axial length of the singlecrystal silicon ingot. Even more preferably, the variation of thenitrogen concentration is not more than about 5% more than and not lessthan 5% less than the set point or average nitrogen concentration overthe axial length of the single crystal silicon ingot. For example, ifthe set point, i.e., the target, nitrogen concentration is 7×10¹³atoms/cm³, preferably, the concentration of nitrogen throughout theaxial length of the single crystal silicon ingot is between about5.67×10¹³ atoms/cm³ and about 8.47×10¹³ atoms/cm³, more preferablybetween about 6.3×10¹³ atoms/cm³ and about 7.7×10¹³ atoms/cm³, and evenmore preferably between about 6.65×10¹³ atoms/cm³ and about 7.35×10¹³atoms/cm³. See FIG. 4B, which is a graph depicting the nitrogenconcentration uniformity (line demarked by open circles ∘) that may beachieved by periodic or continuous addition of nitrogen during anexemplary continuous Czochralski growth according to the method of thepresent disclosure. The uniformity may be compared to the increasingnitrogen concentration observed during a batch growth process (linedemarked by dark circles ●). See also FIG. 2C. Preferably, uniformnitrogen concentration is achieved during growth of all portions of theingot, including the neck portion, the outwardly flaring seed cone, andthe main body. In some embodiments, uniform nitrogen concentration isachieved during growth of at least 40% of axial length of the main bodyof the single crystal silicon ingot, at least 50% of axial length of themain body of the single crystal silicon ingot, at least 60% of axiallength of the main body of the single crystal silicon ingot, at least70% of axial length of the main body of the single crystal siliconingot, or at least 80% of axial length of the main body of the singlecrystal silicon ingot, or at least 90% of axial length of the main bodyof the single crystal silicon ingot.

Once polycrystalline silicon and a source of nitrogen is added to thecrucible to form a charge, the charge is heated to a temperature aboveabout the melting temperature of silicon (e.g., about 1412° C.) to meltthe charge, and thereby form a silicon melt comprising molten silicon.The silicon melt has an initial volume of molten silicon and has aninitial melt elevation level, and these parameters are determined by thesize of the initial charge. In some embodiments, the crucible comprisingthe silicon melt is heated to a temperature of at least about 1425° C.,at least about 1450° C. or even at least about 1500° C. The silicon meltfurther comprises a source of nitrogen sufficient to impart a nitrogendopant concentration in the neck portion of the ingot of at least about1×10¹³ nitrogen atoms/cm³. In some embodiments, silicon melt furthercomprises a source of nitrogen sufficient to impart a nitrogen dopantconcentration in the neck portion of the ingot of between about 1×10¹³atoms/cm³ and about 1×10¹⁵ atoms/cm³, or between about 1×10¹³ atoms/cm³and about 1.5×10¹⁴ atoms/cm³, or between about 5×10¹³ atoms/cm³ andabout 1×10¹⁴ atoms/cm³.

In general, there are no constraints on the resistivity of the singlecrystal silicon ingot. Accordingly, the resistivity of the single singlecrystal silicon ingot is based on the requirements of the enduse/application of the structure of the present disclosure. Theresistivity may therefore vary from milliohm or less to megaohm or more.In some embodiments, the crucible is doped with a p-type or an n-typedopant. Suitable dopants include boron (p type), gallium (p type),phosphorus (n type), antimony (n type), and arsenic (n type). The dopantconcentration is selected based on the desired resistivity of a wafersliced from the single crystal silicon ingot.

In some embodiments, the single crystal silicon ingot pulled accordingto the method of the present disclosure has a relatively low minimumbulk resistivity, such as below about 100 ohm-cm, below about 50 ohm-cm,below about 1 ohm-cm, below about 0.1 ohm-cm, or even below about 0.01ohm-cm. In some embodiments, the single crystal silicon ingot has arelatively low minimum bulk resistivity, such as below about 100 ohm-cm,or between about 1 ohm-cm and about 100 ohm-cm. Low resistivity wafersmay comprise electrically active dopants, such as boron (p type),gallium (p type), phosphorus (n type), antimony (n type), and arsenic (ntype). In some embodiments, the dopants are added to the initial chargein the crucible and resistivity uniformity is maintained by continuousor periodic addition of dopants during crystal growth.

In some embodiments, the single crystal silicon ingot has a relativelyhigh minimum bulk resistivity. The electrically active dopants, such asboron (p type), gallium (p type), aluminum (p type), indium (p type),phosphorus (n type), antimony (n type), and arsenic (n type), may beadded to the crucible in generally very low concentrations. Cz-grownsilicon wafers may be subjected to a thermal anneal at a temperatureranging from about 600° C. to about 1000° C. in order to annihilatethermal donors caused by oxygen that are incorporated during crystalgrowth. In some embodiments, the single crystal silicon ingot has aminimum bulk resistivity of at least 100 Ohm-cm, at least about 500Ohm-cm, at least about 1000 Ohm-cm, or even at least about 3000 Ohm-cm,such as between about 100 Ohm-cm and about 100,000 Ohm-cm, or betweenabout 500 Ohm-cm and about 100,000 Ohm-cm, or between about 1000 Ohm-cmand about 100,000 Ohm-cm, or between about 500 Ohm-cm and about 10,000Ohm-cm, or between about 750 Ohm-cm and about 10,000 Ohm-cm, betweenabout 1000 Ohm-cm and about 10,000 Ohm-cm, between about 2000 Ohm-cm andabout 10,000 Ohm-cm, between about 3000 Ohm-cm and about 10,000 Ohm-cm,or between about 3000 Ohm cm and about 5,000 Ohm-cm. In someembodiments, the single crystal silicon ingot may comprise a p typedopant, such as boron, gallium, aluminum, or indium. In someembodiments, the single crystal silicon ingot may comprise an n typedopant, such as phosphorus, antimony, or arsenic. In some embodiments,the dopants are added to the initial charge in the crucible andresistivity uniformity is maintained by continuous or periodic additionof dopants during crystal growth. For example, in some embodiments, themain body portion has a resistivity that varies by no more than 20%above and no less than 20% below an average main body resistivity overat least 40% of axial length of the main body of the single crystalsilicon ingot, at least 50% of axial length of the main body of thesingle crystal silicon ingot, at least 60% of axial length of the mainbody of the single crystal silicon ingot, at least 70% of axial lengthof the main body of the single crystal silicon ingot, or at least 80% ofaxial length of the main body of the single crystal silicon ingot, or atleast 90% of axial length of the main body of the single crystal siliconingot. In some embodiments, the main body portion has a resistivity thatvaries by no more than 10% above and no less than 10% below an averagemain body resistivity over at least 40% of axial length of the main bodyof the single crystal silicon ingot, at least 50% of axial length of themain body of the single crystal silicon ingot, at least 60% of axiallength of the main body of the single crystal silicon ingot, at least70% of axial length of the main body of the single crystal siliconingot, or at least 80% of axial length of the main body of the singlecrystal silicon ingot, or at least 90% of axial length of the main bodyof the single crystal silicon ingot. In some embodiments, the main bodyportion has a resistivity that varies by no more than 5% above and noless than 5% below an average main body resistivity over at least 40% ofaxial length of the main body of the single crystal silicon ingot, atleast 50% of axial length of the main body of the single crystal siliconingot, at least 60% of axial length of the main body of the singlecrystal silicon ingot, at least 70% of axial length of the main body ofthe single crystal silicon ingot, or at least 80% of axial length of themain body of the single crystal silicon ingot, or at least 90% of axiallength of the main body of the single crystal silicon ingot.

Once the charge is liquefied to form a silicon melt comprising moltensilicon, the silicon seed crystal is lowered to contact the melt. Thesilicon seed crystal is then withdrawn from the melt with silicon beingattached thereto (i.e., the seed crystal portion and neck 52, withreference to FIG. 5) thereby forming a melt-solid interface near or atthe surface of the melt. Generally, the initial pull speed to form theneck portion is high. In some embodiments, the silicon seed crystal andneck portion is withdrawn at a neck portion pull rate of at least about1.0 mm/minute, such as between about 1.5 mm/minute and about 6mm/minute, such as between about 3 mm/minute and about 5 mm/minute. Insome embodiments, the silicon seed crystal and the crucible are rotatedin opposite directions, i.e., counter-rotation. Counter-rotationachieves convection in the silicon melt. Rotation of crystal is mainlyused to provide a symmetric temperature profile, suppress angularvariation of impurities and also to control crystal melt interfaceshape. In some embodiments, the silicon seed crystal is rotated at arate of between about 5 rpm and about 30 rpm, or between about 5 rpm andabout 20 rpm, or between about 8 rpm and about 20 rpm, or between about10 rpm and about 20 rpm. In some embodiments, the crucible is rotated ata rate between about 0.5 rpm and about 10 rpm, or between about 1 rpmand about 10 rpm, or between about 4 rpm and about 10 rpm, or betweenabout 5 rpm and about 10 rpm. In some embodiments, the seed crystal isrotated at a faster rate than the crucible. In some embodiments, theseed crystal is rotated at a rate that is at least 1 rpm higher than therotation rate of the crucible, such as at least about 3 rpm higher, orat least about 5 rpm higher. Conventionally, the crystal rotation rateis higher than the crucible rotation rate, to favor a good radialuniformity of the dopant concentration in the crystal. In someembodiments, the silicon seed crystal and the crucible are rotated inopposite directions, i.e., counter-rotation.

In general, the neck portion has a length between about 10 millimetersand about 700 millimeters, between about 30 millimeters and about 700millimeters, between about 100 millimeters and about 700 millimeters,between about 200 millimeters and about 700 millimeters, or betweenabout 300 millimeters and about 700 millimeters. In some embodiments,the neck portion has a length between about 10 millimeters and about 100millimeters, such as between about 20 and about 50 millimeters. In someembodiments, the neck portion has a length between about 350 millimetersand about 550 millimeters. In some embodiments, the neck portion has alength between about 450 millimeters and about 550 millimeters. However,the length of the neck portion may vary outside these ranges. In someembodiments, the neck portion has a diameter between about 1 mm andabout 10 mm, between about 2.5 mm and about 6.5 mm, such as betweenabout 3 mm and about 6 mm. Since the silicon melt is doped withnitrogen, the neck portion 52 of the ingot is doped with nitrogen. Insome embodiments, the neck portion 52 has a neck portion nitrogenconcentration of at least about 1×10¹³ atoms/cm³. In some embodiments,the neck portion 52 has a nitrogen concentration between about 1×10¹³atoms/cm³ and about 1×10¹⁵ atoms/cm³, or between about 1×10¹³ atoms/cm³and about 1.5×10¹⁴ atoms/cm³, or between about 5×10¹³ atoms/cm³ andabout 1×10¹⁴ atoms/cm³. Preferably, the variation of the nitrogenconcentration is not more than about 20% more than and not less than 20%less than the set point or average nitrogen concentration over the axiallength of the neck portion. More preferably, the variation of thenitrogen concentration is not more than about 10% more than and not lessthan 10% less than the set point or average nitrogen concentration overthe axial length of the neck portion. Even more preferably, thevariation of the nitrogen concentration is not more than about 5% morethan and not less than 5% less than the set point or average nitrogenconcentration over the axial length of the neck portion.

After formation of the neck, the outwardly flaring seed-cone portion 54adjacent the neck 52 is grown, with reference to FIG. 5. In general, thepull rate is decreased from the neck portion pull rate to a ratesuitable for growing the outwardly flaring seed-cone portion. Forexample, the seed-cone pull rate during growth of the outwardly flaringseed-cone is between about 0.5 mm/min and about 2.0 mm/min, such asabout 1.0 mm/min. In some embodiments, the outwardly flaring seed-cone54 has a length between about 100 millimeters and about 400 millimeters,such as between about 150 millimeters and about 250 millimeters. Thelength of the outwardly flaring seed-cone 54 may vary outside theseranges. In some embodiments, the outwardly flaring seed-cone 54 is grownto a terminal diameter of about 150 mm, at least about 150 millimeters,about 200 mm, at least about 200 millimeters, about 300 mm, at leastabout 300 mm, about 450 mm, or even at least about 450 mm. The terminaldiameter of the outwardly flaring seed-cone 54 is generally equivalentto the diameter of the constant diameter of the main body of the singlecrystal silicon ingot. According to the method of the presentdisclosure, the outwardly flaring seed-cone 54 of the ingot is dopedwith nitrogen. In some embodiments, outwardly flaring seed-cone 54 hasan outwardly flaring seed-cone nitrogen concentration of at least about1×10¹³ atoms/cm³. In some embodiments, the outwardly flaring seed-cone54 has a nitrogen concentration between about 1×10¹³ atoms/cm³ and about1×10¹⁵ atoms/cm³, or between about 1×10¹³ atoms/cm³ and about 1.5×10¹⁴atoms/cm³, or between about 5×10¹³ atoms/cm³ and about 1×10¹⁴ atoms/cm³.Preferably, the variation of the nitrogen concentration in the outwardlyflaring seed-cone 54 is not more than about 20% more than and not lessthan 20% less than the set point nitrogen concentration. Morepreferably, the variation of the nitrogen concentration in the outwardlyflaring seed-cone 54 is not more than about 10% more than and not lessthan 10% less than the set point nitrogen concentration. Even morepreferably, the variation of the nitrogen concentration in the outwardlyflaring seed-cone 54 is not more than about 5% more than and not lessthan 5% less than the set point nitrogen concentration. With referenceagain to FIG. 4B, nitrogen concentration uniformity is preferablyachieved according to an exemplary method according to the presentdisclosure during growth of all portions of the ingot, including theoutwardly flaring seed-cone.

After formation of the neck and the outwardly flaring seed-cone adjacentthe neck portion, the main ingot body 56 having a constant diameteradjacent the cone portion is then grown. The constant diameter portionof the main body 56 has a circumferential edge, a central axis that isparallel to the circumferential edge, and a radius that extends from thecentral axis to the circumferential edge. The central axis also passesthrough the cone portion and neck 52. The diameter of the main ingotbody may vary and, in some embodiments, the diameter may be about 150mm, at least about 150 millimeters, about 200 mm, at least about 200millimeters, about 300 mm, at least about 300 mm, about 450 mm, or evenat least about 450 mm. In some embodiments, the main body of the singlecrystal silicon ingot is eventually grown to be at least about 1000millimeters long, such as at least 1100 millimeters long, such as atleast 1200 millimeters long, such as at least 1400 millimeters long,such as at least 1500 millimeters long, such as at least 1700millimeters long, or at least 1900 millimeters long, or at least 2000millimeters long, or at least 2200 millimeters, or at least about 3000millimeters long, or at least about 4000 millimeters long. According tothe method of the present disclosure, the main body 56 of the ingot isdoped with nitrogen. In some embodiments, main body 56 has a main bodynitrogen concentration of at least about 1×10¹³ atoms/cm³. In someembodiments, the main body 56 has a nitrogen concentration between about1×10¹³ atoms/cm³ and about 1×10¹⁵ atoms/cm³, or between about 1×10¹³atoms/cm³ and about 1.5×10¹⁴ atoms/cm³, or between about 5×10¹³atoms/cm³ and about 1×10¹⁴ atoms/cm³. Preferably, the variation of thenitrogen concentration in the main body 56 is not more than about 20%more than and not less than 20% less than the set point nitrogenconcentration. More preferably, the variation of the nitrogenconcentration in the main body 56 is not more than about 10% more thanand not less than 10% less than the set point nitrogen concentration.Even more preferably, the variation of the nitrogen concentration in themain body 56 is not more than about 5% more than and not less than 5%less than the set point nitrogen concentration. With reference again toFIG. 4B, nitrogen concentration uniformity is preferably achievedaccording to an exemplary method according to the present disclosureduring growth of all portions of the ingot, including the main bodyportion. In some embodiments, the main body comprises nitrogen at a mainbody nitrogen concentration that varies by no more than 20% above and noless than 20% below an average main body nitrogen concentration over atleast 40% of axial length of the main body of the single crystal siliconingot, at least 50% of axial length of the main body of the singlecrystal silicon ingot, at least 60% of axial length of the main body ofthe single crystal silicon ingot, at least 70% of axial length of themain body of the single crystal silicon ingot, or at least 80% of axiallength of the main body of the single crystal silicon ingot, or at least90% of axial length of the main body of the single crystal siliconingot. In some embodiments, the main body comprises nitrogen at a mainbody nitrogen concentration that varies by no more than 10% above and noless than 10% below an average main body nitrogen concentration over atleast 40% of axial length of the main body of the single crystal siliconingot, at least 50% of axial length of the main body of the singlecrystal silicon ingot, at least 60% of axial length of the main body ofthe single crystal silicon ingot, at least 70% of axial length of themain body of the single crystal silicon ingot, or at least 80% of axiallength of the main body of the single crystal silicon ingot, or at least90% of axial length of the main body of the single crystal siliconingot. In some embodiments, the main body comprises nitrogen at a mainbody nitrogen concentration that varies by no more than 5% above and noless than 5% below an average main body nitrogen concentration over atleast 40% of axial length of the main body of the single crystal siliconingot, at least 50% of axial length of the main body of the singlecrystal silicon ingot, at least 60% of axial length of the main body ofthe single crystal silicon ingot, at least 70% of axial length of themain body of the single crystal silicon ingot, or at least 80% of axiallength of the main body of the single crystal silicon ingot, or at least90% of axial length of the main body of the single crystal siliconingot.

FIG. 4A illustrates an exemplary and non-limiting pull rate protocol forpulling the main body of the single crystal silicon ingot according tosome embodiments of the method of the present disclosure. As is apparentfrom the exemplary illustration, the pull rate declines from arelatively high pull rate, to a minimum pull rate, and then rising to aconstant pull rate for a significant portion of growth of the main bodyof the single crystal silicon ingot. According to the process of thepresent disclosure, the pull rates are selected to achieve perfectsilicon, i.e., silicon characterized by a lack detectable agglomerateddefects selected from among agglomerated defects, DSOD (direct surfaceoxidation defects), COP (crystal originated pits), D-Defects, andI-defects, etc. The initial high pull rate may be between about 0.5mm/min and about 2.0 mm/min, such as about 1.0 mm/min, then decreasingto a pull rate that may be as low as about 0.4 mm/min or even as low asabout 0.3 mm/min, before increasing to the constant pull rate betweenabout 0.4 mm/min and about 0.8 mm/min, between about 0.4 mm/min andabout 0.7 mm/min, or between about 0.4 mm/min and about 0.65 mm/min.

An exemplary and non-limiting illustration of a hot zone configurationwithin a furnace chamber 100 suitable for carrying out the method of thepresent disclosure is depicted in FIGS. 6A, 6B, and 6C. Other hot zoneconfigurations are suitable for carrying out the method of the presentdisclosure. The hot zone configuration includes a cooling jacket 102, areflector 104, a side heater 106, and a bottom heater 108. The growingcrystal diameter and the shape and height of the meniscus is monitoredby a camera (not pictured) located at the top window. Data obtained fromthe camera enables feedback to the side heater 106 and bottom heater108. During crystal growth, the power distribution may be adjustedbetween the heaters to enable uniformity of the melt/solid interface,i.e., maintain the desired shape and height of the meniscus. Thereflector 104 should reflect the heat flux from the hot part of thefurnace including the heater and crucible to the melt. The reflector 104reduces heat transfer from the hot part to the cold part (maintained bythe cooling jacket 102) of the furnace and thereby maintains aseparation between these two regions of the furnace. The reflector helpscontrol the axial and radial temperature gradients, which drive thesolidification and crystallization of the molten silicon into thegrowing ingot.

FIGS. 6A, 6B, and 6C depict a 1^(st) step, 2^(nd) step, and 3^(rd) step,respectively, corresponding to the regions of pull rate shown in FIG.4A. That is, the 1^(st) step depicted in FIG. 6A corresponds to theregion wherein the pull rate is high and decreases to a minimum in FIG.4A. The 2^(nd) step depicted in FIG. 6B corresponds to the regionwherein the pull rate is at a minimum and increases to the constant pullrate in FIG. 4A. The 3^(rd) step depicted in FIG. 6C corresponds to theregion of constant pull rate in FIG. 4A. During each step, the melt 110retains a constant melt volume and melt elevation level according toembodiments of the present disclosure since polycrystalline silicon iscontinuously fed into the melt (see FIG. 5) during growth of the ingot112.

The initial region of growing the main body of the single crystalsilicon ingot characterized by variable pull rate may encompass lessthan about 20% of the total length of the main body of the singlecrystal silicon ingot. In some embodiments, the variable pull rateregime may encompass between about 5% and about 20% of the length of themain body of the single crystal silicon ingot, such as between about 5%and about 15% of the length of the main body of the single crystalsilicon ingot, or between about 10% and about 15% of the length of themain body of the single crystal silicon ingot. The percentage of thelength of the main body of the single crystal silicon ingot grown undervariable pull rate conditions depends in part on the total length of themain body of the ingot. For example, the length of the main body of theingot pulled under variable rate conditions may vary between about 50 mmto about 200 mm between about 100 mm to about 200 mm, such as betweenabout 150 mm to about 200 mm. If 200 mm is grown under variable rateconditions, and the total length of the main body of the ingot is 1400mm, about 14% of the main body is grown under variable rate conditions,while only about 9% of the main body is grown under variable rateconditions for a total main body length of 2200 mm.

After the initial region of the main body is grown under variable pullrate conditions, the remainder of the main body is grown under aconstant pull rate. In some embodiments, the main body of the ingot isgrown at a constant main body pull rate during growth of at least about30% of the length of the main body of the single crystal silicon ingot,such as at least about 50% of the length of the main body of the singlecrystal silicon ingot, at least about 70% of the length of the main bodyof the single crystal silicon ingot, at least about 80% of the length ofthe main body of the single crystal silicon ingot, or even at leastabout 90% of the length of the main body of the single crystal siliconingot. In some embodiments, the constant main body pull rate is betweenabout 0.4 mm/min and about 0.8 mm/min, between about 0.4 mm/min andabout 0.7 mm/min, or between about 0.4 mm/min and about 0.65 mm/min.

During growth of the main body of the single crystal silicon ingot,polycrystalline silicon, i.e., granular, chunk, or a combination ofgranular and chunk, is added to the molten silicon to thereby achieve aconstant volume of molten silicon and constant melt elevation level.According to the method of the present disclosure, maintenance of asubstantially constant melt volume during growth of a substantialportion of the axial length of the main body of the single crystalsilicon ingot enables the achievement of high ingot quality over asubstantial portion of the axial length of the main body of the singlecrystal silicon ingot at a constant pull rate. The constant melt volumeregardless of the crystal length enables maintaining a constantcrystal/melt interface and thus uniform crystal quality over asubstantial portion of the main body of the ingot. Accordingly, in someembodiments, the volume of molten silicon varies by no more than about1.0 volume % during growth of at least about 90% the main body of thesingle crystal silicon ingot, or by no more than about 0.5 volume %during growth of at least about 90% the main body of the single crystalsilicon ingot, or even by no more than about 0.1 volume % during growthof at least about 90% the main body of the single crystal silicon ingot.Stated another way, in some embodiments, the melt elevation level variesby less than about +/−0.5 millimeter during growth of at least about 90%the main body of the single crystal silicon ingot.

During growth of the main body of the single crystal silicon ingot, themelt is further charged with a source of nitrogen so that the singlecrystal silicon ingot grown according to the method of the presentdisclosure is doped with nitrogen. In some embodiments, the source ofnitrogen is a solid source of nitrogen, such as silicon nitride. Thesilicon nitride may be in the form of a powder. In some embodiments, thesource of nitrogen is a silicon wafer having a silicon nitride film on asurface thereof. The silicon nitride film may be deposited on thesilicon wafer by chemical vapor deposition to deposit, for example, a0.5 to 10 micrometer, such as about 1 micrometer thick film on bothsides of the wafer. The silicon wafer may be added whole or it may becrushed into small pieces. In some embodiments, the source of nitrogenis silicon oxynitride glass. In some embodiments, nitrogen doping may beaccomplished by doping with a nitrogen containing gas, such as nitrogen(N₂) gas. During growth of the ingot, according to the method of thepresent disclosure, the source of nitrogen may be added, along withpolycrystalline silicon, to the third weir 40, as depicted in FIG. 5.

The method of the present disclosure is suitable for achieving axiallyuniform nitrogen concentrations during growth of the neck portion, seedcone, and main body portions of the single crystal silicon ingot. SeeFIG. 4B for a depiction of the uniformity that may be achieved bycontinuous or periodic addition of nitrogen during the growth of theingot according to the continuous Czochralski technique of the presentdisclosure. The uniformity, which overcomes the segregation normallyfound in nitrogen doping single crystal silicon ingots, is achieved byan auto-doping system that continuously or periodically adds a source ofnitrogen to the melt. The source of nitrogen may be added continuouslyor periodically during the growth of the ingot, including each of theneck portion, seed cone, and main body portions. In some embodiment, foruniformity and ease of processing, periodic additions, e.g., duringevery 25 mm, 50 mm, 75 mm, or 100 mm of axial length during ingotgrowth, of the source of nitrogen are preferred. Periodic additions,e.g., during every 25 mm, 50 mm, 75 mm, or 100 mm of axial length duringingot growth, of the source of nitrogen are also preferred in order toenhance attainment of perfect silicon during growth of the axial lengthof the ingot.

In some embodiments, the source of nitrogen is continuously fed orperiodically fed to the crucible in an amount between about 1 milligramnitrogen and about 100 milligrams nitrogen per 50 mm of axial length ofthe main body of the single crystal silicon ingot, or between about 1milligram nitrogen and about 25 milligrams nitrogen per 50 mm of axiallength of the main body of the single crystal silicon ingot, or betweenabout 2 milligrams nitrogen and about 15 milligrams nitrogen per 50 mmof axial length of the main body of the single crystal silicon ingot. Insome embodiments, the source of nitrogen is silicon nitride, which maybe added as a powder. In some embodiments, silicon nitride iscontinuously fed or periodically fed to the crucible during growth ofthe main body of the single crystal silicon ingot in an amount betweenabout 2.5 milligrams silicon nitride and 250 milligrams silicon nitrideper 50 mm of axial length of the main body of the single crystal siliconingot, or between about 5 milligrams silicon nitride and 100 milligramssilicon nitride per 50 mm of axial length of the main body of the singlecrystal silicon ingot, or between about 10 milligrams silicon nitrideand 50 milligrams silicon nitride per 50 mm of axial length of the mainbody of the single crystal silicon ingot. In some exemplary embodiments,between about 10 milligrams and about 50 milligrams, such as about 25milligrams silicon nitride may be added per 50 mm of axial length of amain body having a nominal diameter of about 310 millimeters. The amountof silicon nitride added may be scaled up or down depending upon thenominal diameter of the ingot. For example, between about 1 milligramsand about 10 milligrams, such as about 5 or 6 milligrams silicon nitridemay be added per 50 mm of axial length of a main body having a nominaldiameter of about 150 millimeters. In yet another example, between about25 milligrams and about 75 milligrams, such as between about 45milligrams and about 60 milligrams silicon nitride may be added per 50mm of axial length of a main body having a nominal diameter of about 450millimeters. An exemplary feeding protocol displaying total additions ofsilicon nitride as a function of axial length of the single crystalsilicon ingot is depicted in FIG. 7.

In some embodiments, the source of nitrogen is added during growth toachieve a main body nitrogen concentration between about 1×10¹³atoms/cm³ and about 1×10¹⁵ atoms/cm³, or between about 1×10¹³ atoms/cm³and about 1.5×10¹⁴ atoms/cm³, or between about 5×10¹³ atoms/cm³ andabout 1×10¹⁴ atoms/cm³. In some embodiments, the source of nitrogen isadded during growth to achieve a main body nitrogen concentrationbetween about 5×10¹³ atoms/cm³ and about 1×10¹⁴ atoms/cm³, over at least40% of axial length of the main body of the single crystal siliconingot, at least 50% of axial length of the main body of the singlecrystal silicon ingot, at least 60% of axial length of the main body ofthe single crystal silicon ingot, at least 70% of axial length of themain body of the single crystal silicon ingot, or at least 80% of axiallength of the main body of the single crystal silicon ingot, or at least90% of axial length of the main body of the single crystal siliconingot, or even at the entire axial length of the main body of the singlecrystal silicon ingot.

In some embodiments, the source of nitrogen is added during growth toachieve a main body nitrogen concentration between about 1×10¹³atoms/cm³ and about 1.5×10¹⁴ atoms/cm³, or between about 5×10¹³atoms/cm³ and about 1×10¹⁴ atoms/cm³ and further wherein the main bodynitrogen concentration varies by no more than 20% above and no less than20% below a set point or an average main body nitrogen concentrationover at least 40% of axial length of the main body of the single crystalsilicon ingot, at least 50% of axial length of the main body of thesingle crystal silicon ingot, at least 60% of axial length of the mainbody of the single crystal silicon ingot, at least 70% of axial lengthof the main body of the single crystal silicon ingot, or at least 80% ofaxial length of the main body of the single crystal silicon ingot, or atleast 90% of axial length of the main body of the single crystal siliconingot, or even at the entire axial length of the main body of the singlecrystal silicon ingot. More preferably, the variation of the nitrogenconcentration in the main body 56 is not more than about 10% more thanand not less than 10% less than the set point nitrogen concentrationover at least 40% of axial length of the main body of the single crystalsilicon ingot, at least 50% of axial length of the main body of thesingle crystal silicon ingot, at least 60% of axial length of the mainbody of the single crystal silicon ingot, at least 70% of axial lengthof the main body of the single crystal silicon ingot, or at least 80% ofaxial length of the main body of the single crystal silicon ingot, or atleast 90% of axial length of the main body of the single crystal siliconingot, or even at the entire axial length of the main body of the singlecrystal silicon ingot. Even more preferably, the variation of thenitrogen concentration in the main body 56 is not more than about 5%more than and not less than 5% less than the set point nitrogenconcentration over at least 40% of axial length of the main body of thesingle crystal silicon ingot, at least 50% of axial length of the mainbody of the single crystal silicon ingot, at least 60% of axial lengthof the main body of the single crystal silicon ingot, at least 70% ofaxial length of the main body of the single crystal silicon ingot, or atleast 80% of axial length of the main body of the single crystal siliconingot, or at least 90% of axial length of the main body of the singlecrystal silicon ingot, or even at the entire axial length of the mainbody of the single crystal silicon ingot.

In some embodiments, the source of nitrogen is added during growth toachieve a main body nitrogen concentration between about 5×10¹³atoms/cm³ and about 1×10¹⁴ atoms/cm³ and further wherein the main bodynitrogen concentration varies by no more than 20% above and no more than20% below a set point or an average main body nitrogen concentrationover at least 40% of axial length of the main body of the single crystalsilicon ingot, at least 50% of axial length of the main body of thesingle crystal silicon ingot, at least 60% of axial length of the mainbody of the single crystal silicon ingot, at least 70% of axial lengthof the main body of the single crystal silicon ingot, or at least 80% ofaxial length of the main body of the single crystal silicon ingot. Morepreferably, the variation of the nitrogen concentration in the main body56 is not more than about 10% more than and not less than 10% less thanthe set point nitrogen concentration over at least 40% of axial lengthof the main body of the single crystal silicon ingot, at least 50% ofaxial length of the main body of the single crystal silicon ingot, atleast 60% of axial length of the main body of the single crystal siliconingot, at least 70% of axial length of the main body of the singlecrystal silicon ingot, or at least 80% of axial length of the main bodyof the single crystal silicon ingot, or at least 90% of axial length ofthe main body of the single crystal silicon ingot, or even at the entireaxial length of the main body of the single crystal silicon ingot. Evenmore preferably, the variation of the nitrogen concentration in the mainbody 56 is not more than about 5% more than and not less than 5% lessthan the set point nitrogen concentration over at least 40% of axiallength of the main body of the single crystal silicon ingot, at least50% of axial length of the main body of the single crystal siliconingot, at least 60% of axial length of the main body of the singlecrystal silicon ingot, at least 70% of axial length of the main body ofthe single crystal silicon ingot, or at least 80% of axial length of themain body of the single crystal silicon ingot, or at least 90% of axiallength of the main body of the single crystal silicon ingot, or even atthe entire axial length of the main body of the single crystal siliconingot.

Additionally, according to the process of the present disclosure, amagnetic field may be applied to the crucible comprising the siliconmelt. Either cusp or horizontal magnet field can be applied to set theappropriate crystal/melt interface, i.e., the shape and height of themeniscus. The magnetic field is used to fix a desire crystal/meltinterface shape and height primarily, and control of the oxygen content,Oi, is a subordinate purpose.

Control of the melt flow and the shape of the melt/solid interface andtherefore the quality of the ingot may be enhanced by the application ofa magnetic field to the silicon melt during growth of the main body ofthe single crystal silicon ingot. In some embodiments, the appliedmagnetic field maintains a substantially constant melt/solid interfaceprofile during at least about 70% of the growth of the main body of thesingle crystal silicon ingot, or between about 70% and about 90% of thegrowth of the main body of the single crystal silicon ingot. Themagnetic field applies electromagnetic force, which affects the siliconmelt flow, so the heat transfer in the melt is affected. It changes theprofile of crystal/melt interface and the temperature of growingcrystal, which are the key control parameter of perfect silicon.

The magnetic field impacts the oxygen content and uniformity in theingot. The source of oxygen is the ingot is from dissolution of thequartz crucible wall, evaporation SiOx (g) at the melt free surface(controlled by melt flow kinetics) and incorporation into growingcrystal front. The magnet field impacts the convective melt flow duringgrowth which can impact Oxygen evaporation and incorporation. Thevariation of oxygen incorporation into the single crystal silicon ingotby time increment is controlled by the diffusion and convection ofoxygen in the melt according to the following equation:

$\frac{\partial C}{\partial t} = {{\nabla C} - {v\;\rho} + {{SOURCE}.}}$

C is the concentration of oxygen is the solidifying silicon, t is time,v is the convection velocity (melt flow velocity), rho, ρ, is thedensity of silicon melt, ∇ is the gradient (d/dx). The applied magneticfield affects the melt velocity (v) and the gradient of oxygenconcentration in the melt (dC/dx=∇C). Since magnetic field results in asteady state melt flow, the incorporating of oxygen, Oi, into the ingotis time constant, which enhances radial and axial oxygen concentrationuniformity. The SOURCE term is derived from two parameters, thedissolution of quartz (SiO₂) crucible which is the generation of oxygen(Si (1)+SiO2(s)→SiOx(g)), and the evaporation which is the removal(disappearance) of oxygen (SiOx(g)) from melt. In a batch Cz process,this SOURCE term is not constant. Instead, it depends upon the crystallength since the melt mass decreases as the crystal is grown. When theingot has grown a substantial portion of its body length, the remainingmelt volume is low, so that that amount of silicon melt in contact withthe crucible is decreased, which therefore leads to lower concentrationsof oxygen incorporated from the crucible into the melt. Therefore, theoxygen incorporated into solidifying silicon crystal is decreased, ifother terms (diffusion, convection, evaporation) are constant. The meltfree surface (contact surface between melt and gas) area affects theevaporation rate of SiOx(g). A small melt mass in a batch Cz process hasrelatively smaller surface area due to shape of crucible as shown inFIG. 1C. Less evaporation of SiOx(g) means more oxygen incorporationinto the solidifying silicon crystal. According to the method of thepresent disclosure, the melt mass is maintained as constant sincepolysilicon is added as the crystal ingot grows. Accordingly, all sourceterms (generation of Oxygen by SiO₂ crucible dissolution into melt, andevaporation of SiOx(g) gas through melt free surface) are constant.Therefore, the diffusion and convection terms affect the oxygen ofsolidifying silicon crystal. The applied magnetic field makes melt flowmore stable (i.e., melt flow is constant like as time independent steadycondition), so incorporating Oxygen is uniform and stable in the axialand radial directions during growth of the entire length of the ingot.In some embodiments, interstitial oxygen may be incorporated into theingot in a concentration between about 4 PPMA and about 18 PPMA. In someembodiments, interstitial oxygen may be incorporated into the ingot in aconcentration between about 10 PPMA and about 35 PPMA. In someembodiments, the ingot comprises oxygen in a concentration of no greaterthan about 15 PPMA, or no greater than about 10 PPMA. Interstitialoxygen may be measured according to SEMI MF 1188-1105. In someembodiments, the main body interstitial oxygen concentration that variesby no more than 20% above and no less than 20% below an average mainbody oxygen concentration over at least 40% of axial length of the mainbody of the single crystal silicon ingot, at least 50% of axial lengthof the main body of the single crystal silicon ingot, at least 60% ofaxial length of the main body of the single crystal silicon ingot, atleast 70% of axial length of the main body of the single crystal siliconingot, or at least 80% of axial length of the main body of the singlecrystal silicon ingot, or at least 90% of axial length of the main bodyof the single crystal silicon ingot. In some embodiments, the main bodyinterstitial oxygen concentration that varies by no more than 10% aboveand no less than 10% below an average main body oxygen concentrationover at least 40% of axial length of the main body of the single crystalsilicon ingot, at least 50% of axial length of the main body of thesingle crystal silicon ingot, at least 60% of axial length of the mainbody of the single crystal silicon ingot, at least 70% of axial lengthof the main body of the single crystal silicon ingot, or at least 80% ofaxial length of the main body of the single crystal silicon ingot, or atleast 90% of axial length of the main body of the single crystal siliconingot. In some embodiments, the main body interstitial oxygenconcentration that varies by no more than 5% above and no less than 5%below an average main body oxygen concentration over at least 40% ofaxial length of the main body of the single crystal silicon ingot, atleast 50% of axial length of the main body of the single crystal siliconingot, at least 60% of axial length of the main body of the singlecrystal silicon ingot, at least 70% of axial length of the main body ofthe single crystal silicon ingot, or at least 80% of axial length of themain body of the single crystal silicon ingot, or at least 90% of axiallength of the main body of the single crystal silicon ingot.

In some embodiments, a horizontal magnetic field is applied to thesilicon melt during growth of the main body of the single crystalsilicon ingot. Such a horizontal field is illustrated in FIG. 8A, whichis a depiction of a horizontal magnetic field superimposed over thecrucible and growing ingot as depicted in FIG. 5. Crystal growth inpresence of a horizontal magnetic field is achieved by placing thecrucible holding the silicon melt between the poles of a conventionalelectromagnet 200. In some embodiments, the horizontal magnetic fieldmay have a magnetic flux density between about 0.2 Tesla and about 0.4Tesla in the melt area. Magnetic field variation in the melt is lessthan +/−about 0.03 Tesla in a given strength. Application of ahorizontal magnetic field gives rise to Lorentz force along axialdirection, in a direction opposite of fluid motion, opposing forcesdriving melt convection. The convection in the melt is thus suppressed,and the axial temperature gradient in the crystal near the interfaceincreases. The melt-crystal interface then moves upward to the crystalside to accommodate the increased axial temperature gradient in thecrystal near the interface and the contribution from the melt convectionin the crucible decreases.

In some embodiments, a cusp magnetic field is applied to the siliconmelt during growth of the main body of the single crystal silicon ingot.A cusp field is illustrated in FIG. 8B, which is a depiction of a cuspmagnetic field superimposed over the crucible and growing ingot asdepicted in FIG. 5. A cusp magnetic field has two controllingparameters, namely the magnetic flux density and magnetic field shape. Acusp magnetic field applies a horizontal (radial) magnetic fieldcomponent at the nearest surface of the melt combined with a vertical(axial) magnetic field deeper in the melt near the axis of the ingot.The cusp magnetic field is generated using a pair of Helmholtz coilcarrying current in opposite direction. As a result, at the positionhalfway between the two magnetic fields, vertically along the ingotaxis, the magnetic fields cancel each other out to make a verticalmagnetic field component at or near zero. For example, the cusp magneticflux density is typically about zero to about 0.2 Tesla in the axialdirection. The magnetic flux density in the radial direction isgenerally higher than the magnetic flux density in the verticaldirection. For example, the cusp magnetic flux density is typicallybetween about 0 and about 0.6T in the radial position, such as betweenabout 0.2 and about 0.5T, dependent upon the radial position. The radialcusp magnetic field restrains the flow of the melt, to thereby stabilizethe melt. In other words, application of a radial cusp magnetic fieldinduces convection at a portion adjacent to the solid-liquid interfaceat which crystal growth occurs, and suppresses convection at theremaining portions of the melt, to thereby serve as an effective methodfor realizing uniform oxygen distribution. Thermal melt convection canbe locally and independently controlled by the cusp magnetic field atthe melt free surface and at the melt crucible interface at the sametime. This enables to control the oxygen concentration in the growingcrystal by magnetic flux density only, irrespective of crystal rotationspeed. In presence of an axial or a radial magnetic field, control ofoxygen concentration is achieved via control of crystal rotation speed.Application of the cusp magnetic field may enable growth on an ingotcomprising less oxygen content than an ingot grown without an appliedmagnetic field, such as no greater than about 15 PPMA, or no greaterthan about 10 PPMA. Interstitial oxygen may be measured according toSEMI MF 1188-1105.

The method of the present disclosure enables growth of single crystalsilicon ingots by the continuous Czochralski method meeting or exceedingindustry specifications for perfect silicon. Factors contributing to thegrowth of perfect silicon crystals include determining the critical pullspeed for growing perfect silicon, maintaining a constant pull speed atthe critical speed over a substantial portion of the growth of the mainbody of the single crystal silicon ingot, and applying a magnetic fieldto maintain the shape and height of the melt/solid interface. Once theconfigurations of pull speed and magnetic field are determined, the pullspeed may be maintained at a constant rate due to the continuousaddition of polycrystalline silicon to maintain a constant melt volumeand melt elevation level. Accordingly, unlike conventional methods ofgrowing ingots, the pull speed is constant over a substantial portion ofthe growth of the ingot. In view of the process controls enabled by themethod disclosed herein, the method of the present disclosure enablesthe growth of a single crystal silicon ingot comprising perfect siliconover at least about 70% of the length of the main body of the singlecrystal silicon ingot, such as over at least about 80% of the length ofthe main body of the single crystal silicon ingot, or even over at leastabout 90% of the length of the main body of the single crystal siliconingot.

As used herein, the terms “about,” “substantially,” “essentially” and“approximately” when used in conjunction with ranges of dimensions,concentrations, temperatures or other physical or chemical properties orcharacteristics is meant to cover variations that may exist in the upperand/or lower limits of the ranges of the properties or characteristics,including, for example, variations resulting from rounding, measurementmethodology or other statistical variation.

When introducing elements of the present disclosure or the embodiment(s)thereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” “containing” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. The use of terms indicating a particular orientation (e.g.,“top”, “bottom”, “side”, etc.) is for convenience of description anddoes not require any particular orientation of the item described.

As various changes could be made in the above constructions and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawing[s] shall be interpreted as illustrative and not ina limiting sense.

We claim:
 1. A method of preparing a single crystal silicon ingot by theContinuous Czochralski method, the method comprising: adding an initialcharge of polycrystalline silicon to a crucible, the initial chargefurther comprising a source of nitrogen; heating the crucible comprisingthe initial charge of polycrystalline silicon and the source of nitrogento cause a silicon melt to form in the crucible, the silicon meltcomprising an initial volume of molten silicon and having an initialmelt elevation level; contacting a silicon seed crystal with a siliconmelt; withdrawing the silicon seed crystal to grow a neck portion,wherein the silicon seed crystal is withdrawn at a neck portion pullrate during growth of the neck portion, and further wherein the neckportion has a neck portion nitrogen concentration of at least about1×10¹³ atoms/cm³; withdrawing the silicon seed crystal to grow anoutwardly flaring seed-cone adjacent the neck portion, wherein thesilicon seed crystal is withdrawn at a seed-cone pull rate during growthof the outwardly flaring seed-cone, and further wherein the outwardlyflaring seed-cone has an outwardly flaring seed-cone nitrogenconcentration of at least about 1×10¹³ atoms/cm³; and withdrawing thesilicon seed crystal to grow a main body of the single crystal siliconingot adjacent the outwardly flaring seed-cone, wherein the silicon meltcomprises a volume of molten silicon and a melt elevation level duringgrowth of the main body of the single crystal silicon ingot, and furtherwherein the main body of the single crystal silicon has a main bodynitrogen concentration of at least about 1×10¹³ atoms/cm³, wherein themain body of the single crystal silicon ingot is at least about 1000millimeters long; wherein the main body of the single crystal siliconingot is grown at an initial variable main body pull rate and a constantmain body pull rate, wherein the main body of the single crystal siliconingot is grown at the initial variable main body pull rate for less thanabout 20% of a length of the main body of the single crystal siliconingot and grown at the constant main body pull rate during growth for atleast about 30% of the length of the main body of the single crystalsilicon ingot, wherein the constant main body pull rate is between about0.4 mm/min and about 0.8 mm/min, and further wherein the main body ofthe single crystal silicon ingot has a diameter of at least about 150millimeters; wherein a magnetic field is applied to the silicon meltduring growth of the main body of the single crystal silicon ingot, andfurther wherein the main body of the single crystal silicon ingotcomprises a main body interstitial oxygen concentration between about 10PPMA and about 35 PPMA, and further wherein the main body interstitialoxygen concentration varies by no more than 20% above and no less than20% below an average main body oxygen concentration over at least 60% ofaxial length of the main body of the single crystal silicon ingot; andfurther wherein polycrystalline is continuously fed or periodically feedto the crucible to thereby replenish a volume of molten silicon and tothereby maintain a melt elevation level in the crucible during growth ofthe main body of the single crystal silicon ingot and the source ofnitrogen is continuously fed or periodically fed to the crucible tothereby replenish an amount of nitrogen.
 2. The method of claim 1wherein the source of nitrogen is a solid source of nitrogen.
 3. Themethod of claim 1 wherein the source of nitrogen is nitrogen gas.
 4. Themethod of claim 1 wherein the source of nitrogen is continuously fed orperiodically fed to the crucible in an amount between about 1 milligramnitrogen and about 100 milligrams nitrogen per 50 mm of axial length ofthe main body of the single crystal silicon ingot.
 5. The method ofclaim 1 wherein silicon nitride is continuously fed or periodically fedto the crucible during growth of the main body of the single crystalsilicon ingot in an amount between about 2.5 milligrams silicon nitrideand 250 milligrams silicon nitride per 50 mm of axial length of the mainbody of the single crystal silicon ingot.
 6. The method of claim 1wherein a horizontal magnetic field is applied to the silicon meltduring growth of the main body of the single crystal silicon ingot. 7.The method of claim 1 wherein a cusp magnetic field is applied to thesilicon melt during growth of the main body of the single crystalsilicon ingot.
 8. The method of claim 1 wherein the applied magneticfield maintains a substantially constant melt/solid interface profileduring at least about 70% of the growth of the main body of the singlecrystal silicon ingot.
 9. The method of claim 1 wherein the appliedmagnetic field maintains a substantially constant melt/solid interfaceprofile during between about 70% and about 90% of the growth of the mainbody of the single crystal silicon ingot.
 10. The method of claim 1wherein the main body of the single crystal silicon ingot is at least1400 millimeters long and has a diameter of at least about 200millimeters.
 11. The method of claim 1 wherein the constant main bodypull rate is between about 0.4 mm/min and about 0.7 mm/min.
 12. Themethod of claim 1 wherein the main body of the single crystal siliconingot is grown at the initial variable main body pull rate for betweenabout 5% and about 20% of the length of the main body of the singlecrystal silicon ingot.
 13. The method of claim 1 wherein the main bodyof the single crystal silicon ingot is grown at the constant main bodypull rate during growth for at least about 50% of the length of the mainbody of the single crystal silicon ingot.
 14. The method of claim 1wherein the main body of the single crystal silicon ingot is grown atthe constant main body pull rate during growth for at least about 70% ofthe length of the main body of the single crystal silicon ingot.
 15. Themethod of claim 1 wherein the main body of the single crystal siliconingot is grown at the constant main body pull rate during growth for atleast about 90% of the length of the main body of the single crystalsilicon ingot.
 16. The method of claim 1 wherein the main body pull rateis a constant critical pull rate sufficient to avoid agglomerated pointdefects over at least 70% of the length of the main body of the singlecrystal silicon ingot.
 17. The method of claim 1 wherein the main bodypull rate is a constant critical pull rate sufficient to avoidagglomerated point defects over at least 90% of the length of the mainbody of the single crystal silicon ingot.
 18. The method of claim 1wherein the volume of molten silicon varies by no more than about 1.0volume % during growth of at least about 90% the main body of the singlecrystal silicon ingot.
 19. The method of claim 1 wherein the volume ofmolten silicon varies by no more than about 0.5 volume % during growthof at least about 90% the main body of the single crystal silicon ingot.20. The method of claim 1 wherein the volume of molten silicon varies byno more than about 0.1 volume % during growth of at least about 90% themain body of the single crystal silicon ingot.
 21. The method of claim 1wherein the melt elevation level varies by less than about +/−0.5millimeter during growth of at least about 90% the main body of thesingle crystal silicon ingot.
 22. The method of claim 1 wherein the mainbody of the single crystal silicon ingot comprises perfect silicon overat least about 70% of the length of the main body of the single crystalsilicon ingot.
 23. The method of claim 1 wherein the main body of thesingle crystal silicon ingot comprises perfect silicon over at leastabout 90% of the length of the main body of the single crystal siliconingot.
 24. A method of preparing a single crystal silicon ingot by theContinuous Czochralski method, the method comprising: adding an initialcharge of polycrystalline silicon to a crucible, the initial chargefurther comprising a source of nitrogen; heating the crucible comprisingthe initial charge of polycrystalline silicon and the source of nitrogento cause a silicon melt to form in the crucible, the silicon meltcomprising an initial volume of molten silicon and having an initialmelt elevation level; contacting a silicon seed crystal with a siliconmelt; withdrawing the silicon seed crystal to grow a neck portion,wherein the silicon seed crystal is withdrawn at a neck portion pullrate during growth of the neck portion, and further wherein the neckportion has a neck portion nitrogen concentration of at least about1×10¹³ atoms/cm³; withdrawing the silicon seed crystal to grow anoutwardly flaring seed-cone adjacent the neck portion, wherein thesilicon seed crystal is withdrawn at a seed-cone pull rate during growthof the outwardly flaring seed-cone, and further wherein the outwardlyflaring seed-cone has an outwardly flaring seed-cone nitrogenconcentration of at least about 1×10¹³ atoms/cm³; and withdrawing thesilicon seed crystal to grow a main body of the single crystal siliconingot adjacent the outwardly flaring seed-cone, wherein the silicon meltcomprises a volume of molten silicon and a melt elevation level duringgrowth of the main body of the single crystal silicon ingot, and furtherwherein the main body of the single crystal silicon has a main bodynitrogen concentration of at least about 1×10¹³ atoms/cm³, wherein themain body of the single crystal silicon ingot is at least about 1000millimeters long, and further wherein the main body portion has aresistivity between about 1000 Ohm-cm and about 100,000 Ohm-cm andfurther wherein the resistivity varies by no more than 20% above and noless than 20% below an average main body resistivity over at least 60%of axial length of the main body of the single crystal silicon ingot;wherein the main body of the single crystal silicon ingot is grown at aninitial variable main body pull rate and a constant main body pull rate,wherein the main body of the single crystal silicon ingot is grown atthe initial variable main body pull rate for less than about 20% of alength of the main body of the single crystal silicon ingot and grown atthe constant main body pull rate during growth for at least about 30% ofthe length of the main body of the single crystal silicon ingot, whereinthe constant main body pull rate is between about 0.4 mm/min and about0.8 mm/min, and further wherein the main body of the single crystalsilicon ingot has a diameter of at least about 150 millimeters; andfurther wherein polycrystalline is continuously fed or periodically feedto the crucible to thereby replenish a volume of molten silicon and tothereby maintain a melt elevation level in the crucible during growth ofthe main body of the single crystal silicon ingot and the source ofnitrogen is continuously fed or periodically fed to the crucible tothereby replenish an amount of nitrogen.
 25. The method of claim 24wherein the source of nitrogen is a solid source of nitrogen.
 26. Themethod of claim 24 wherein the source of nitrogen is nitrogen gas. 27.The method of claim 24 wherein the source of nitrogen is continuouslyfed or periodically fed to the crucible in an amount between about 1milligram nitrogen and about 100 milligrams nitrogen per 50 mm of axiallength of the main body of the single crystal silicon ingot.
 28. Themethod of claim 24 wherein silicon nitride is continuously fed orperiodically fed to the crucible during growth of the main body of thesingle crystal silicon ingot in an amount between about 2.5 milligramssilicon nitride and 250 milligrams silicon nitride per 50 mm of axiallength of the main body of the single crystal silicon ingot.
 29. Themethod of claim 24 wherein a magnetic field is applied to the siliconmelt during growth of the main body of the single crystal silicon ingot,and further wherein the main body of the single crystal silicon ingotcomprises a main body interstitial oxygen concentration between about 10PPMA and about 35 PPMA, and further wherein the main body interstitialoxygen concentration varies by no more than 20% above and no less than20% below an average main body oxygen concentration.
 30. The method ofclaim 29 wherein a horizontal magnetic field is applied to the siliconmelt during growth of the main body of the single crystal silicon ingot.31. The method of claim 29 wherein a cusp magnetic field is applied tothe silicon melt during growth of the main body of the single crystalsilicon ingot.
 32. The method of claim 29 wherein the applied magneticfield maintains a substantially constant melt/solid interface profileduring at least about 70% of the growth of the main body of the singlecrystal silicon ingot.
 33. The method of claim 29 wherein the appliedmagnetic field maintains a substantially constant melt/solid interfaceprofile during between about 70% and about 90% of the growth of the mainbody of the single crystal silicon ingot.
 34. The method of claim 24wherein the main body of the single crystal silicon ingot is at least1400 millimeters long and has a diameter of at least about 200millimeters.
 35. The method of claim 24 wherein the constant main bodypull rate is between about 0.4 mm/min and about 0.7 mm/min.
 36. Themethod of claim 24 wherein the main body of the single crystal siliconingot is grown at the initial variable main body pull rate for betweenabout 5% and about 20% of the length of the main body of the singlecrystal silicon ingot.
 37. The method of claim 24 wherein the main bodyof the single crystal silicon ingot is grown at the constant main bodypull rate during growth for at least about 50% of the length of the mainbody of the single crystal silicon ingot.
 38. The method of claim 24wherein the main body of the single crystal silicon ingot is grown atthe constant main body pull rate during growth for at least about 70% ofthe length of the main body of the single crystal silicon ingot.
 39. Themethod of claim 24 wherein the main body of the single crystal siliconingot is grown at the constant main body pull rate during growth for atleast about 90% of the length of the main body of the single crystalsilicon ingot.
 40. The method of claim 24 wherein the main body pullrate is a constant critical pull rate sufficient to avoid agglomeratedpoint defects over at least 70% of the length of the main body of thesingle crystal silicon ingot.
 41. The method of claim 24 wherein themain body pull rate is a constant critical pull rate sufficient to avoidagglomerated point defects over at least 90% of the length of the mainbody of the single crystal silicon ingot.
 42. The method of claim 24wherein the volume of molten silicon varies by no more than about 1.0volume % during growth of at least about 90% the main body of the singlecrystal silicon ingot.
 43. The method of claim 24 wherein the volume ofmolten silicon varies by no more than about 0.5 volume % during growthof at least about 90% the main body of the single crystal silicon ingot.44. The method of claim 24 wherein the volume of molten silicon variesby no more than about 0.1 volume % during growth of at least about 90%the main body of the single crystal silicon ingot.
 45. The method ofclaim 24 wherein the melt elevation level varies by less than about+/−0.5 millimeter during growth of at least about 90% the main body ofthe single crystal silicon ingot.
 46. The method of claim 24 wherein themain body of the single crystal silicon ingot comprises perfect siliconover at least about 70% of the length of the main body of the singlecrystal silicon ingot.
 47. The method of claim 24 wherein the main bodyof the single crystal silicon ingot comprises perfect silicon over atleast about 90% of the length of the main body of the single crystalsilicon ingot.